Existing phase noise measurement techniques typically provide an aggregate measurement of so-called pure phase noise and phase noise from other sources induced on a radio frequency (RF) signal. The pure phase noise may be induced by components of a transmitter, such as an oscillator for example. The phase noise from other sources may originate from complex valued noise sources, and may include thermal noise, or various kinds of modulation-induced and synchronization-induced noise signals which may originate from a transmission filter, a non-ideal IQ modulator or timing uncertainty. It has been commonly accepted in the industry that pure phase noise and other phase noise induced on an RF signal can not be distinguished from each other, and generally can not be measured individually.
In the field of telecommunications, there is a need to measure phase noise induced by transmitters on complex digitally modulated signals such as wideband code division multiple access (WCDMA) and orthogonal frequency-division multiplexing (OFDM) signals including wireless local area network (LAN) signals and long term evolution (LIE) signals, as a way of testing the transmitters. However, such phase noise from the various other sources may mask the pure phase noise that is of interest for measurement. Existing phase noise measurement techniques typically do not have the ability to separately and accurately measure pure phase noise induced on RE signals.
There is therefore a need to provide improved phase noise extraction apparatuses and techniques that can distinguish between various types of phase noise and provide accurate measurement of pure phase noise.